Electrolytic capacitors (e.g., tantalum capacitors) are increasingly being used in the design of circuits due to their volumetric efficiency, reliability, and process compatibility. For example, one type of capacitor that has been developed is a solid electrolytic capacitor that includes an anode (e.g., tantalum), a dielectric oxide film (e.g., tantalum pentoxide, Ta2O5) formed on the anode, a solid electrolyte layer, and a cathode. The solid electrolyte layer may be formed from a conductive polymer, such as described in U.S. Pat. No. 5,457,862 to Sakata, et al., U.S. Pat. No. 5,473,503 to Sakata, et al., U.S. Pat. No. 5,729,428 to Sakata, et al., and U.S. Pat. No. 5,812,367 to Kudoh, et al. Unfortunately, however, the stability of such solid electrolytes is poor at high temperatures due to the tendency to transform from a doped to an un-doped state, or vice versa. In response to these and other problems, capacitors have been developed that are hermetically sealed to limit the contact of oxygen with the conductive polymer during use. U.S. Patent Publication No. 2009/0244812 to Rawal, et al., for instance, describes a capacitor assembly that includes a conductive polymer capacitor that is enclosed and hermetically sealed within a ceramic housing in the presence of an inert gas. The housing includes a lid that is welded to the sidewalls of a base structure. According to Rawal, et al., the ceramic housing limits the amount of oxygen and moisture supplied to the conductive polymer so that it is less likely to oxidize in high temperature environments, thus increasing the thermal stability of the capacitor assembly.
Despite the benefits achieved, however, problems nevertheless remain. For example, high capacitance applications generally require a large anode size to achieve the desired capacitance. Due to its large size, however, the capacitor element is mechanically instable, particularly under extreme conditions (e.g., high temperature of above about 175° C. and/or high voltage of above about 35 volts), which leads to leading to delamination and poor electrical performance.
As such, a need currently exists for a capacitor that is capable of achieving a high capacitance and yet remain stable even under extreme conditions.